Start game - freeze before main menu - black or distorted graphics

[dave_k]

Summary
After upgrading to a new version, multiple users have experienced a problem where the game seems to be frozen and has black or distorted video output. User-installed mods seem to trigger this problem.

Removing all user-installed mod files seems to resolve the problem, but should only be considered a workaround. I think that this bug will still be experienced by users in the future due to design flaws in the game startup sequence.

Visual proof
See attached screenshots.

Expected vs. actual results
Expected results: The game starts up, displays the main menu and thematic artwork, and plays music. The main menu responds to mouse clicks and the game functions correctly.

Actual results: The game starts, and the game window is all black or else very garbled with strange colors and a collage of various parts of the windows on the desktop. Mouse input has no effect other than moving the 0ad-themed mouse cursor around. No audio plays, not even music, despite resetting the user configuration.

Tirili is one such user who has experienced this problem. Based on a debugging session with Tirili, the main game loop is actually running, and the game responds correctly to keyboard input such as F2 for taking a screenshot. But the game is not usable.

Steps to reproduce
First, if you are using Debian or a Debian-derived distribution of Linux such as Ubuntu, ensure that 0ad-data was not built with dh_strip_nondeterminism enabled for .zip files. This ensures reliable reproduction of the symptoms.

Then, extract the attached file, "Tirili 0ad dot local share 0ad files aka 0adRenamed3.tar.gz", to /home/<yourusername>/.local/share/0ad/, or the equivalent Windows folder for user mods.

Environnment
Two users have reported this problem so far, Tirili and Farid.
Tirili uses GNU/Linux. Slackware distribution. AMD APU (CPU combined with GPU) that is approximately 6 months old.
Farid uses GNU/Linux. Unknown distribution and hardware.
And, I am able to reproduce the symptoms with Debian GNU/Linux. Intel CPU and nVIDIA GPU.

Console logs
See attached file, "2021-08-21 bug report from Tirili - backtrace.txt". Note that the current source line in the backtrace is just where it happened to be at the time that I asked Tirili to press Ctrl-C in order to obtain a backtrace. The game loop is able to continue normally and calls to Render() and LimitFPS() complete. Yet the game window video output remains black (or garbled, depending on the test environment).

Related tickets
I plan to post additional tickets for the following related issues.

1. Add diagnostics: listing files accessed and gui error messages on console and in log file instead of only in graphical window. The latter can't be read if the GUI is not working correctly.
   
2. Add ability to enable verbose startup, error and warning messages or logging.
   
3. Add detection of broken mods and offer to reset mod configuration. Or, support a command line switch to reset the mod configuration. Or, support a command line switch to enable "safe mode" where mods are disabled, and advanced graphics features are also disabled.

[dave_k]

Example symptoms on dave_k's computer

[dave_k]

Example symptoms on dave_k's computer